Resonance-Enhanced Multiphoton Ionisation Time-of-Flight Mass Spectrometry

Resonance-Enhanced Multiphoton Ionisation Time-of-Flight Mass Spectrometry 

Selective and time-resolved monitoring can be achieved by REMPl at 266 nm coupled to a direct-inlet TOFMS device. Selectivity was introduced into the ionisation step by resonant ionisation at a fixed UV laser wavelength. The photoexcitation energy scheme for REMPl is illustrated in Fig. 15.20. 

Depending on molecular resonances, VOCs with an optical (electronic) absorption at 266 nm absorb a laser photon, while those transparent at 266 nm remain in the ground state. The width of optical absorptions is given by the ground-state population, and broadens with the molecules temperature, which itself depends on the expansion conditions at the inlet system. 

Since an elfusive molecular beam was used (no cooling), a range of rotational and vibrational states was populated, resulting in broad absorption bands. Consequently, a range of compounds maybe ionised simultaneously, owing to overlapping absorption bands [200].Technical reviews on REMPI can be found in the literature [200-202]. 

In a typical REMPI scheme, molecules absorb a first photon and are excited into a UV electronic state. These excited molecules are subsequently ionised by absorbing a second photon. For effective and selective REMPI detection, the following conditions have to be fulfilled  

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MOS metal oxide sensor, MOSFET metal oxide semiconductor field-effect transistor, IR infrared, CP conducting polymer, QMS quartz crystal microbalance, IMS ion mobility spectrometry, BAW bulk acoustic wave, MS mass spectrometry, SAW siuface acoustic wave, REMPI-TOFMS resonance-enhanced multiphoton ionisation time-of-flight mass spectrometry... 

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